1. Field of the Invention
Embodiments of the present invention relate to an optical pickup and corresponding actuator having a multi-conductive suspension, and more particularly, to a multi-conductive suspension for an optical pickup having a plurality of stiff conductive metals lined up on a flexible substrate, and an optical pickup actuator having the same.
2. Description of the Related Art
In general, optical pickups can be employed in optical recording/reproducing apparatuses and may enable recording and/or reproducing of information to/from a disk mounted on a turntable while moving in a radial direction of the disk. Such an optical pickup can include an objective focusing a beam emitted from a light source to form an optical spot on an optical disk, and an actuator controlling the objective in a track direction, a focus direction, and a tilt direction to direct the optical spot to a precise location on the optical disk.
FIG. 1 illustrates a perspective view of an actuator. Referring to FIG. 1, a conventional optical pickup actuator includes a base 100, a holder 103 fixed to the base 100, a bobbin 107 for holding an objective 105, a plurality of suspension wires 130 connected between the bobbin 107 and the holder 103 for supporting the bobbin 107, and a magnetic driving unit driving the bobbin 107 in a track direction, a focus direction, and/or a tilt direction. In this case, the suspension wires 130 support the bobbin 107 and draw the bobbin 107 against the holder 103. In addition, the magnetic driving unit can be formed of magnets 110 arranged on the base 100 and a plurality of coils 120, 122, and 125 arranged on the bobbin 107. The bobbin 107 can be driven by an electromagnetic force generated by applying currents to the coils 120, 122, and 125, within a magnetic field generated by the magnets 110. The suspension wires 130 may also transmit the currents to the coils 120, 122, and 125, in addition to supporting the bobbin 107.
However, as the recording capacity of recording media have increased, the resolution required by an optical pickup has accordingly increased, such that the degree of freedom of a corresponding actuator should be increased. In general, when one degree of freedom is increased, the number of coils arranged on the bobbin 107 is increased by one, resulting in an increase of the number of wires applying currents to the coils, by two. For example, in the case of an optical pickup actuator for a blu-ray disk (BD), which has a high recording density, seven wires may be used, including two focusing wires, two tracking wires, and three liquid crystal panel wires for spherical aberration compensation. As the number of wires is increased, the number of the suspension wires 130, operating as the wires, should also be increased. In the case of the optical pickup actuator for the BD, eight suspension wires may be used, as the suspension wires 130 connected to both sides of the bobbin 107 can be kept in symmetry.
In this case, the eight wires can be formed to operate as suspensions having a supporting stiffness. In another case, a portion of the eight wires can be operated as suspensions having a supporting stiffness while another portion of the eight wires can be operated as current providing wires for the coils.
When all eight wires operate as suspensions having supporting stiffness, four wires can be soldered on both sides of the bobbin 107. Accordingly, as the number of soldered portions increases, the assembly of an actuator correspondingly deteriorates and the DC offset tilt and the natural tilt of the actuator become degraded. Furthermore, when the number of wires is increased, the number of the suspension wires should be similarly increased; however, it may become impossible to add a number of suspension wires while still maintaining the present bobbin size. For example, when an additional function, such as the control of radial tilt, is added, the required number of wires becomes nine, and the required number of suspension wires becomes ten, if the aforementioned symmetry is maintained. Thus, five suspension wires can be soldered on both sides of the bobbin. Further, since a predetermined distance should be maintained between the wires to prevent shorts between adjacent wires, it becomes impossible to add the necessary number of suspension wires without increasing the size of the bobbin. However, an increase of the bobbin size results in the increase of the size of the actuator.
On the other hand, when some of the wires operate as suspension wires having supporting stiffness while other wires operate as wires for providing current to the coils, the wires can be easily formed. However, when the suspension wires and the coil wires are separated, assembly processes are increased and shorts may occur between the coil wires or between the suspension wires and the coil wires, resulting in degradation of reliability and increased assembly measures. In addition, the coil wires may not be firmly attached to the bobbin, which may further degrade the overall reliability.